Solvent tipping of polyethylene terephthalate filaments



United States Patent Office 3,422,180 Patented Jan. 14, 1969 3,422,180SOLVENT TIPPING OF POLYETHYLENE TEREPHTHALATE FILAMENTS Doyce B. Hanson,John E. Hansen, and Nolan D. Boyer,

Wilmington, Del., assignors to E. I. du Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware No Drawing. Filed Oct. 21,1965, Ser. No. 500,211 US. Cl. 264-341 1 Claim Int. Cl. D011? 7 /06;A46d 1/04 ABSTRACT OF THE DISCLOSURE Preparation of tipped bristles ofpolyethylene terephthalate, by repeatedly dipping and withdrawing abundle of the bristles from a solvent for polyethylene terephthalate.The preferred solvent is 40% tetrachloroethane and 60% phenol. Thepreferred temperature for this solvent is 50 to 70 C.

This invention relates to the modifying of synthetic filaments for useas bristles, and more particularly, to a process for tipping offilaments of polyethylene terephthalate for use as bristles.

The preparation of filaments from polyethylene terephthalate has beendescribed in Whinfield et al., US. Patent 2,465,319. The production ofmonofils thereof for use as bristles by a drawing and heat-settingprocess has been described in McClellan, US. Patent 2,615,784. A methodof producing improved bristles consists of forming tapered filamentsaccording to Fields, US. Patent 2,423,182, and then mechanically tippingthe filaments to a slender point. However, mechanical tipping offilaments of polyethylene terephthalate with commercial abrasive tippingmachines is not practical, since the filaments are readily damagedtherein. Therefore, alternative tipping techniques are desirable.

This invention provides a solvent-dipping method for tipping tapered oruntapered filaments of polyethylene terephthalate fiber for use asbristles. The tipping is accomplished in accordance with this inventionby repeated dipping of a bundle of polyethylene terephthalate filamentsin a solution. It would generally be expected that such treatment of abundle of filaments with a solvent would result in fusion of thefilaments to a solid mass. However, after the dipping operation asdescribed herein, the surprising result is that the filaments arereadily separable and each filament appears to have a pencil-point tip,as shown by photomicrographs.

A bundle of filaments is tipped according to this invention by repeatedlowering into and raising from a solvent bath. The filaments used may beeither level (untapered) or tapered at the start. The degree of taperingof the filaments may vary widely; the invention lies in the tipping ofthe filaments.

Any of the known solvents for polyethylene terephthalate can be usedwithin the scope of this invention, for example, phenol, m-cresol, orvariations proportions of mixed solvent systems, for exampletetrachloroethanephenol. The tetrachloroethane-phenol solvent system ispreferred, and, for best results, a mixture of 40% tetrachloroethane and60% phenol is employed for the tipping bath.

The temperature of the tipping bath should be below the softeningtemperature of the filaments and can be varied from room temperature tothe boiling point of the solvent or solvent mixture employed within thelimits of the above proviso. Better results are obtained with warmsolvent systems (40100 C.). With the preferred solvent of thisinvention, 40% tetrachloroethane60% phenol, a temperature in the 5070 C.range is preferred.

With a fresh tipping solution, a bath temperature of 60 C. gives thebest results.

The duration of the dipping operation can be varied depending, amongother things, upon the rate of dipping, the solvent employed, and thebath temperature. With 40% tetrachloroethane-60% phenol held at about50-70" C., a dipping time of 10 to 30 minutes is preferred. With a freshsolution of the latter, best results are obtained with dipping period ofabout 20 minutes. After the dipping treatment, the filamentsare washedwith any solvent in which polyethylene terephthalate is insoluble and inwhich the tipping solution is soluble. Preferably, the solvent for thetipping solution is water-soluble, so that, after the tipping solutionhas been washed off, the bundle of filaments can then be rinsed withwater and dried. For example, methanol, ethanol, acetone, or methylethyl ketone can be used to remove the tipping solution. However,water-insoluble solvents for the tipping solutioncan also be used, suchas benzene, toluene, dichloromethane, chloroform, and carbontetrachloride, after which the filaments are dried. The preferredwashing operation consists of first rinsing the filaments with methanolto remove the tipping solution, followed by rinsing with water to removethe methanol.

In order that the invention may be better understood, the followingdetailed examples are given in addition to the examples already givenabove.

Example 1 Filaments of polyethylene terephthalate with taper ratios(diameter of butt end to that of tapered end) of either 7/4 or 9/5 andof a uniform length (varying between 3% and 4 /2 inches from run to run)were gathered into pound bundles approximately 2 inches in diameter atthe butt end.

The bundle was clamped at the butt end to an oifset mounted on the shaftof a clock motor which revolved at 2 rpm, thereby raising and loweringthe bundle. A vessel containing a solution composed of 40%tetrachloroethane and 60% phenol (by weight) was arranged so that thetips of the filaments were submerged to a depth of /2 inch at the.bottom of the stroke, and were completely removed from, the solution atthe top of the stroke. With the tetrachloroethane-phenol solution heldat 60 the bundle was subjected to the cyclic dipping and withdrawingtreatment for 20 minutes, then flushed with methanol from the butt endto the tip end so as to wash solution out of the bundle without exposingthe butt end to the dipping solution. After repeated washing with freshmethanol the bundle was thoroughly rinsed with water, then placed in avacuum oven at room temperature for 16 hours with a nitrogen sweep. Thefilaments were easily separable, and each appeared to have apencil-point tip.

Example 2 A 4-inch paint brush constructed from untipped, but taperedpolyethylene terephthalate bristles was treated by the method of Example1, with the result that the bristles were likewise tipped.

While the invention has been described with particular reference tospecific embodiments, it will be appreciated that no unnecessarylimitations are to be understood therefrom. The invention is not limitedto the exact details shown and described, since obvious modificationswill occur to those skilled in the art.

We claim:

1. A process of tipping polyethylene terephthalate filaments for use asbristles which comprises dipping only the tip of a bundle ofpolyethylene terephthalate filaments into a solvent mixture of 40%tetrachloroethane and the remainder phenol, the temperature of thesolvent being about 5070 C., withdrawing the tip from the solvent,

about 20 minutes.

References Cited UNITED FOREIGN PATENTS 1,107,637 5/1961 Germany.

STATES PATENTS JULIUS FROME, Primary Examiner. whi fi ld et 1 2 0.45 5A. H. KOECKERT, Assistant Examiner.

Watson 2 75 Rieber 260 75 US. Cl. X.R. MacAllister. 156-7, 2

